Superhydrophobic Silicone Rubber Surfaces Research Articles

Temperature-dependent droplet impact dynamics of a water droplet on hydrophobic and superhydrophobic surfaces: An experimental and predictive machine learning–based study

• Droplet impact on microstructured surfaces (hydrophobic/superhydrophobic) at different temperatures has been studied. • Effect of velocity, droplet diameter, temperature, surface wettability and roughness on impact dynamic are evaluated. • Using three machine-learning algorithms, an innovative method for predicting droplet impact dynamic is presented. Heightening the water repellency of surfaces can serve anti-icing purposes by removing water drops before they freeze and adhere to a surface. Here we study the impact dynamics of water droplets on silicone rubber surfaces—ranging from hydrophobic to superhydrophobic—at −20, −10, and 25 °C. We evaluate the influence of static contact angle, contact angle hysteresis, surface roughness, temperature, impacting velocity, and droplet diameter on droplet behavior (e.g., deposition, bouncing, splash). Minor effect of temperature on droplet dynamics on microstructured surfaces for a wide range of Weber and Reynolds numbers is observed. Experimental observations show that full bouncing only occurs on superhydrophobic surfaces with a CA > 160° and a CAH < 2° at temperatures above 0 °C for We < 110 and Re < 5000. Increasing the impact velocity of the droplet on rough surfaces heightens the probability of splashing. This experimental data is then coupled with machine-learning techniques (logistic regression, decision tree, and random forest) to comprehensively investigate droplet impact behavior on hydrophobic and superhydrophobic surfaces at various temperatures. We predict the behavior probability of impacting droplets on surfaces as a function of Weber number, Reynolds number and surface features (static contact angle, contact angle hysteresis, temperature, and surface roughness). Our experimental results and machine learning–based predictions are highly consistent, demonstrating that machine learning can effectively predict droplet motion on hydrophobic and superhydrophobic silicone rubber surfaces at different temperatures.

Aging Characteristics of Superhydrophobic Silicone Rubber Surfaces Etched by Femtosecond Laser

Aging Characteristics of Superhydrophobic Silicone Rubber Surfaces Etched by Femtosecond Laser

Aging characteristics and self-healing properties of laser-textured superhydrophobic silicone rubber for composite insulators

The aging characteristics of laser-treated superhydrophobic silicone rubber surfaces was investigated through accelerated aging tests. It indicated that the superhydrophobic surfaces have excellent anti-aging properties, which is manifested in that even after aging for 1000 h, the contact angles of the superhydrophobic surfaces remain above 140o. The loss of hydrophobicity was caused by defects in the surface microstructures, a decrease in the hydrophobic ―CH3 groups, and an increase in the hydrophilic ―OH groups on the surfaces. To avoid the decrease in the hydrophobicity of the prepared superhydrophobic surface, a simple and efficient heat treatment method was adopted to restore its hydrophobicity. After heat treatment at 200°C, the rolling angle of the aged surface was restored to 4.6o with a contact angle of 161.5o. This recovery is mainly attributed to the decrease in the content of the ―OH on the rubber surface during the heat treatment. The results also show the sample surface irradiated with a laser fluence of 10.0 J/cm2 has better anti-aging performance and self-healing properties due to the larger particles and a more distinct micro-nano hierarchical structures, providing a smaller actual illumination area and a larger heating area in the aging and heat treatment process.

纳秒激光诱导超疏水硅橡胶表面微结构的分形特性

纳秒激光诱导超疏水硅橡胶表面微结构的分形特性

A fluorine-free superhydrophobic silicone rubber surface has excellent self-cleaning and bouncing properties

Superhydrophobic materials have been widely applied in self-cleaning, anti-fouling, anti-corrosion, anti-freezing. However, simple, efficient, environmentally friendly and large-area preparation is still a great challenge in the field of fabrication of superhydrophobic surfaces. In this paper, a simple physical deposition method is adopted to deposit a layer of alumina oxide (Al2O3) particles on the surface of the room temperature vulcanized (RTV) silicone rubber, and remove the excess Al2O3 particles on the surface to obtain the superhydrophobic surface of Al2O3/RTV silicone rubber. The contact angle and rolling angle of the superhydrophobic surface are 156.6° ± 1.1° and 5.1° ± 0.7°, respectively. It is found that the surface roughness of RTV silicone rubber is significantly increased via Al2O3 particles. The analysis of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) demonstrate that the superhydrophobic surface is obtained via constructing rough structure of Al2O3 particles on the RTV silicone rubber surface. In addition, the self-cleaning and droplet bounce tests under different conditions show that the as-prepared superhydrophobic surface has remarkable self-cleaning and droplet bounce properties. Therefore, this method can be employed to simply and effectively fabricate superhydrophobic surfaces in large scale.

Icephobicity and durability assessment of superhydrophobic surfaces: The role of surface roughness and the ice adhesion measurement technique

The durability of anti-wetting properties is of great importance for ensuring long-lasting superhydrophobic and icephobic surfaces that require minimal maintenance and resurfacing. Herein, we fabricated superhydrophobic silicone rubber surfaces having ultra-water repellency and icephobic properties via two industrially applicable methods: micro compression molding (μCM) and atmospheric pressure plasma (APP) treatment. We produced surfaces covered by micro-nanostructures of differing sizes. We evaluated the anti-icing properties (delayed ice formation) and de-icing properties (reduced ice adhesion strength) of the produced surfaces that were subjected to two forms of icing conditions. The well-known ice adhesion measurement techniques, i.e., the centrifuge adhesion and push-off tests, provided quantitative comparisons of the ice adhesion strength of the produced surfaces. We observed two different mechanical deformations during the ice detachment from the surfaces. Although both superhydrophobic surfaces reduced ice adhesion strength, the smaller surface micro-nanostructures produced a greater reduction in ice adhesion by favoring less ice interlocking with the surface asperities. To rigorously assess the durability of the produced surfaces, we carried out a comprehensive series of experiments that covered a wide range of real-life conditions. Under harsh environmental conditions, the surfaces maintained a water contact angle and contact angle hysteresis of >150° and <10°, respectively, thereby confirming the resistance of the superhydrophobic silicone surfaces to severe chemical and mechanical damage. In some cases where water repellency was lost, the silicone rubber surfaces demonstrated a satisfactory recovery of their anti-wetting properties.

Superhydrophobic silicone rubber surface prepared by direct replication

ABSTRACT The superhydrophobic surface of silicone rubber was prepared by means of a simple direct replication and compression moulding process. It was worth noting that the rough structure endowed the surface of the silicone rubber with excellent superhydrophobic, low adhesion and self-cleaning properties. The contact angle with water was 158.5 ± 0.5°, and the rolling angle was 8.9 ± 0.1°. Even if immersed in water, the surface will not become wetted by the water. In addition, it has excellent properties of hydrophobic hydrochloric acid solution, sodium hydroxide solution and sodium chloride solution. Through a high-speed camera, it was found that water droplets would bounce up after falling on the superhydrophobic surface of the silicone rubber. When the liquid drops fall perpendicular to the superhydrophobic surface of silicone rubber, the time of contact between the liquid drops and the superhydrophobic surface is not inversely proportional to the height of the drop falling.

Icing performance of superhydrophobic silicone rubber surfaces by laser texturing

In this paper, the superhydrophobic surfaces of silicone rubber with different microstructure were directly prepared by texturing with a nanosecond fibre laser. The superhydrophobic surfaces have excellent anti-icing performance. Even at 0 °C, the superhydrophobic surface has a contact angle of ∼150° and a rolling-off angle of ∼2.5°. The superhydrophobic silicone rubber surfaces with different microstructures have obvious differences in contact behaviours with water droplets at low temperatures. The surface textured with a laser fluence of 10 J cm−2 has a larger particle size and more abundant micro-nano particles, which results in a smaller contact area with the water droplet due to greater roughness and root mean square slope. The deeper the small gaps on the superhydrophobic surface, the more time it takes for the change in contact state between the surface and the water droplets. The adhesion strength of the superhydrophobic rubber surfaces with the ice layer were smaller due to the air stored between the surfaces and the ice layer. In particular, the laser textured surface with an laser fluence of 10 J cm−2 has the lowest ice adhesion strength due to its layered micro-nano composite structure. After 30 cycles of icing and de-icing, the processed silicone rubber surface still retains excellent hydrophobicity. The superhydrophobic silicone rubber surface has important value in anti-icing and anti-pollution applications.

Simple Fabrication of Superhydrophobic Surfaces Using Atmospheric-Pressure Plasma

Nature-inspired superhydrophobic surfaces have received immense industrial and academic interest due to their non-wettability and self-cleaning properties. To fabricate superhydrophobic silicone rubber surfaces, a simple, environmentally friendly atmospheric-pressure plasma treatment was applied. The effect of diverse plasma processing parameters on the final wettability behavior of the substrates, including plasma power, plasma frequency, number of passes, plasma jet speed, plasma cycle time and distance between the nuzzle outlet and substrate, were analyzed by means of design of experiments (DoE). Surface chemical characterization illustrated the influence of plasma treatment on the chemical composition of the produced silicone rubber. Furthermore, the presence of microstructures as well as the chemical composition of the surface was confirmed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analysis.

Direct replication of micro-nanostructures in the fabrication of superhydrophobic silicone rubber surfaces by compression molding

We describe a simple method for fabricating superhydrophobic high temperature vulcanized (HTV) silicone rubber surfaces by direct replication using a compression molding system. The resulting rubber samples possessed micro-nanostructures on the surface. This micro- and nano-scale roughness produced a water contact angle of >160° and a contact angle hysteresis of <3°. The roughness patterns on chemically etched aluminum surfaces, which served as templates, were successfully replicated on the rubber surfaces. An antistiction coating applied to the template surface ensured that the rubber was completely removed during demolding and that the replicated micro-nanostructures on the silicone surface were preserved. Surface roughness of the aluminum templates was optimized at HCl concentrations of 15 wt.%, with a lower roughness value observed at acid concentrations above and below this value. The developed HTV silicone rubber surfaces also demonstrated a freezing delay and a self-cleaning capacity.

Effect of superhydrophobicity on surface damage of silicone rubber under AC voltage

In this paper, the influence of superhydrophobicity on the surface damage of silicone rubber is studied. On a common silicone rubber surface, a droplet can become elongated, and arc discharge induced by the droplet can cause tracking on the silicone rubber surface. However, for a superhydrophobic silicone rubber surface, a droplet can leave the silicone rubber due to the low adhesion of the superhydrophobic surface. Accordingly, arc discharge caused by the droplet does not occur, and the surface of the silicone rubber is not affected. Results demonstrate that using a superhydrophobic surface has a significant effect on limiting the surface damage of silicone rubber.

Effect of superhydrophobicity on flashover characteristics of silicone rubber under wet conditions

Superhydrophobic surface has aroused much interest among researchers due to the low adhesion between water and a substrate surface. This study focuses on the influence of the low adhesion of superhydrophobic surface on flashover characteristics under wet conditions. The flashover experiments were conducted under two different wet conditions. One was placing a constant volume droplet on the silicone rubber. The other one was that silicone rubber was wetted by salt fog. It was found that the adhesion between water droplets and a superhydrophobic surface was very low because of the presence of air cushion. Accordingly, water droplets were easy to slide on a superhydrophobic surface under the effect of electric filed. The sliding of droplets could provide a longer insulation path before flashover occurred. Results showed that flashover voltage could be improved greatly on a superhydrophobic silicone rubber surface.

Dynamic behavior of water droplets and flashover characteristics on a superhydrophobic silicone rubber surface

In this paper, a superhydrophobic surface is used to increase the flashover voltage when water droplets are present on a silicone rubber surface. The dynamic behavior of a water droplet and the associated flashover characteristics are studied on common and superhydrophobic silicone rubber surfaces under a high DC voltage. On common silicone rubber, the droplet elongates and the flashover voltage decreases with increasing droplet volume and conductivity. In contrast, the droplet slides off the superhydrophobic surface, leading to an increased flashover voltage. This droplet sliding is due to the low adhesion of the superhydrophobic surface and a sufficiently high electrostatic force provided by the DC voltage. Experimental results show that a superhydrophobic surface is effective at inhibiting flashover.